Replying to Weirdest Boner

So last night I was using a TENS Machine to work my hamstring as I had torn a fiber a few weeks back and it was aggravated. I don't know why but I got this idea in my head to put it on the shaft of my penis. So input the "-" patch on the base and the "+" patch on the head of my penis.

Within seconds of turning it on I felt a weird tingling feeling and my penis went from flaccid to rock hard within the next few seconds.

Wondering can you finish using this? It was pretty intense; don't want to do damage